[3H]‐auxin (0.13 to 0.18 nmol) was applied to the apical bud of broadbean plants (Vicia faba L. cv. Aguadulce). After 24 h, the exportation from the donor organ was ended. After 48 h, i.e. 10–15 h after the passage of the [3H]‐auxin pulse into the root system, the distribution and the nature of labelled molecules located in the basal part of the stem and in the axillary buds were investigated. Chromatographic analyses concerned both intact plants and plants decapitated 12 h, 24 h or 42 h after the [3H]‐auxin application. In intact plants, there was no significant amount of [3H]‐auxin in the axillary buds, whose radioactivity was very low compared to the stem tissues. The labelled molecules with the Rf of auxin represented 50% or more of the whole radioactivity of the stem tissues. The distribution of [3H]‐auxin was not uniform along the stem. In particular, the cotyledonary node zone, bearing the most inhibited buds, which is known to be an important centre of label retention, contained the highest amounts of labelled auxin both in intact and decapitated plants. The decapitation was quickly followed by a decrease of the [3H]‐auxin amount in the stem base more than 15 cm away from the wound, particularly in the scale leaf nodes, whose axillary buds were mainly the ones to grow after relief from apical dominance. The induction of this early decrease was clearly distinct in plants decapitated when auxin exportation from the donor organ was ended.

Leaflet movements of Cassia fusciculata are induced by transferring lcavcs from light to darkness or from darkness to light. Phytochrome mediates the dark-induced closure whereas a blue and far red light absorbing pigment (cryptochrome?) is the photoreceptor triggering the light-induced opening. These movements are the result of reversible turgor variation driven by ionic migrations (H+. K + , Cl~-) in cortical parenchyma cells of motor organs ("pulvini") localized at the leaflet base. Calcium plays a predominant role in the regulation of the movements ac shown by the inhibitory effects of chelators (EDTA, EGTA), intracellular antagonist TMB-X and by the promoting cffcct of ionophore A 23 187. Compounds known as calcium channel blockers (LaCI,, verapamil and nifedipine) inhibited whereas Bay K 8644, a calcium channel activator, promoted the phytochromc-mediated movement. In contrast, all these calcium channel modulators had no effect on the blue pigmentmediated movement. From these results, it is suggested that calcium is not mobilized in the same manner in the two types of movements: possibly from external stores in the phytochrome-mediated response and from internal stores in the blue pigment-mediated response. Calcium acts possibly through calmodulin as suggested by a modification in the kinetics of the movements induced by inhibitors of calmodulin action (trifuoperazine, R 24571, W-7). The unexpected promotion of the movements by these inhibitors shows that calmodulin action on the ion migrations is not simple and direct. Experimental observations suggested that regulation might be done through CAMP metabolism. db-CAMP promoted the movements. Compounds known either to xtivate adenylate cyclase (prostaglandins, forskolin) or to inhibit phosphodiesterase (imidazolidinones, ICI 58301) induced the same modifications as db-CAMP. By contrast, a phosphodiesterase activator (imidazole) inhihitcd the movements

No abstract

Levels of endogenous abscisic acid (ABA; free and bound forms) have been determined by gas chromatography in stems and buds of broad‐bean plants (Vicia faba L. cv. Aguadulce) in relation to apical dominance. A downward gradient of free cis‐trans ABA occurred along the stem, from the apical bud to the roots. Except for the actively growing apical bud the levels of free cis‐trans ABA were higher in the buds than in the corresponding nodes. An inverse correlation can be set up between levels of free cis‐trans ABA and growth of buds, except for the cotyledonary ones. High levels of bound ABA (cis‐trans form) are correlated with the growth of the apical bud and that of the axillary bud ax1. The hormonal regulation of the growth of the cotyledonary buds, which contained high levels of trans‐trans ABA in bound forms, is apparently different from that of the other buds.

Endogenous levels of abscisic acid (ABA) were measured by gas‐liquid chromatography (electron capture) in stems and axillary buds of intact or decapitated broad‐bean plants (Vicia faba L. cv. Aguadulce). Endogenous ABA was distributed in the main axis according to a concentration gradient from the apical part of the stem towards the base. Axillary buds contained ABA levels which were from 4 to 9 times higher than those in the corresponding nodes and internodes. Decapitation of the plant was followed within 6 h by a large decrease of ABA levels in all the parts of the main axis. The diminution of ABA content was the most important in axillary buds released from apical dominance. Twenty‐four hours after the decapitation, the ABA concentration further decreased in the upper parts of the stem, while no modification was observed in the basal parts of the stem containing the smallest levels of ABA.